Proportional flow control valve

ABSTRACT

A proportional flow control valve that has a main valve member controlling communication between an inlet and an outlet and a pilot valve in communication with the fluid inlet. A spring biases the main valve member into its closed position against the pressure of the fluid at the inlet which is applied to the main valve member in a direction to open the valve. The fluid pressure within the pilot chamber opposes opening of the valve. A magnetic armature which can be positioned in a selected longitudinal position is provided to open the valve. As fluid pressure is applied to both sides of the main valve member, it is the longitudinal position of the armature which determines the longitudinal position of the main valve member. The main valve member has a converging portion extending with a tubular member, on one end of which the fluid outlet is defined. Changing the position of the converging portion within the tubular member changes the area of the flow path and hence the rate of flow of fluid through the valve. Thus, the fluid flow rate through the valve is determined by the position of the armature and this, in turn, is determined by the amplitude of electrical current applied to the armature.

BACKGROUND OF THE INVENTION

The present invention relates to a method and system for dispensingfluids, and to a sensor, transducer and proportional valve for use insuch a system or with such a method.

To avoid the need to transport and store water, it is becoming common todispense beverages, for example, by mixing a concentrate with water atthe point of sale. However, the resultant beverages dispensed by thesystems which are currently available are generally variable in quality.For example, if water and concentrate are dispensed from individualpipes, but at more than one location, the resultant pressure drops andviscosity variations change the water to concentrate volumetric ratio ofthe beverage being dispensed. In this respect, currently availablemechanical means for controlling the flow of a liquid during a dispensecannot be made to react to changes in the pressure drop, viscosity orflow rate of the liquids.

It is an object of the present invention to provide a method and systemfor reliably dispensing fluids, which method and system reduces thedisadvantages of the known systems. The invention also seeks to providecomponent parts for such a system.

According to a first aspect of the present invention, there is provideda piezoelectric sensor for a sonic transducer, the sensor comprising ahousing defining an opening, a piezoelectric element comprising apiezoelectric film mounted to extend across the opening, electricallyconductive regions contacting opposed surfaces of the piezoelectric filmand overlying to define one area of the piezoelectric film at which theopposed conductive regions coincide, and means for making electricalconnections to said conductive regions, wherein the means for makingelectrical connections comprises an electrically conductive postextending within the housing, an end surface of the post contacting onesurface of the piezoelectric film at the one area thereof.

When electrical signals for example, electrical pulses are applied tothe electrically conductive regions, it is only at the one area of thepiezoelectric film that the pulse is applied across the thickness of thepiezoelectric film. Accordingly, it is only at the one area thatmechanical deformation takes place. A sensor of the invention is therebyable to output a sound wave from the one area only. Preferably, thesensor of the invention is arranged to output an ultrasonic waveform.

The electrically conductive post which is arranged to contact the onesurface of the piezoelectric film acts to maximise the ultrasonic wavesemitted.

The electrically conductive regions may be defined, for example, byelectrically conductive films provided on opposing surfaces of thepiezoelectric film. In this case, the end surface of the electricallyconductive post contacts the electrically conductive film provided onthe one surface of the piezoelectric film.

However, it is presently preferred that the end surface of the postdirectly contacts the one surface of the piezoelectric film and thusdefines one of the electrically conductive regions. In this case, it isalso presently preferred that the other electrically conductive regionis defined by an electrically conductive film provided on the othersurface of the piezoelectric film.

Any suitable piezoelectric film may be utilized.

In a preferred embodiment of the invention, it is preferred that thepiezoelectric film be a film of polvinylidene fluoride (PVDF).

In a preferred embodiment the electrically conductive film is preferablya film of gold. Not only is gold conductive, it is also inert, and thislatter property is clearly important if the sensor is to be used, forexample, in a transducer to measure the properties of a beverage.

In an embodiment, the electrically conductive film is applied to the oreach surface of the piezoelectric film by vapour deposition.

If electrically conductive film is applied to both surfaces of thepiezoelectric film, one surface of the piezoelectric film may beentirely covered with the electrically conductive film except for asingle cutout, whilst the other surface may have a small area only ofelectrically conductive film, at least part of which does not coincidewith the cutout. The at least part of the small area of the electricallyconductive film on the other surface will thereby define with theelectrically conductive film on the first surface thereof the one areaof the piezoelectric element.

Preferably, the one area of the piezoelectric film is substantiallycircular. It is also preferred that the circular area is locatedsubstantially centrally of the piezoelectric film.

In a preferred embodiment, the piezoelectric film is generally circular.

The means for making electrical connections to the electricallyconductive regions preferably comprises at least the opening of saidhousing, the opening being arranged to surround and contact theperiphery of one of the surfaces of the piezoelectric film. Theconductive post extends substantially transversely with respect to thepiezoelectric film.

Preferably, the piezoelectric element is supported on a plasticsmaterial body which is received within the housing.

The plastics material body is preferably substantially cylindrical andmay be provided with an axial bore therethrough in which the conductivepost extends, the bore extending substantially centrally of the plasticsbody. Electrical connections may be made directly the conductive post orby way of an electrical terminal also extending within the plasticsbody.

Although it is possible to form a plastics material body andsubsequently to insert appropriate posts and terminals therein it ispresently preferred that the plastics material body has been formed bybeing moulded around the conductive post.

The invention also extends to a method of forming a piezoelectricsensor, the method comprising the steps of moulding a plastics materialbody around a conductive post, machining one surface of the body andpost, affixing a piezoelectric film onto the machined surface such thata machined end of the post is electrically connected to one surface ofthe piezoelectric film, providing an electrically conductive region onthe other surface of the piezoelectric film, and mounting the body, postand film in a housing.

According to a further aspect of the present invention there is provideda flow transducer for measuring the flow rate of a fluid, the flowtransducer comprising an elongate measuring chamber along which a fluidis arranged to flow, an upstream sensor at an upstream end of themeasuring chamber, and a downstream sensor at a downstream end of themeasuring chamber, wherein each of the sensors is controllable to emitand/or receive a sound beam and is arranged such that sound beamsemitted pass along the measuring chamber, and wherein the measuringchamber is substantially linear, and is arranged to diverge in thedirection of fluid flow.

Preferably, a section of the measuring chamber at the upstream endthereof is tapered inwardly in the direction of fluid flow. This avoidsthe formation of a vena contractor.

The invention also extends to a flow transducer for measuring the flowrate of a fluid, the flow transducer comprising an elongate measuringchamber along which a fluid is arranged to flow, an upstream sensor atan upstream end of the measuring chamber, and a downstream sensor at adownstream end of the measuring chamber, wherein each of the sensors iscontrollable to emit and/or receive a sound beam and is arranged suchthat sound beams emitted pass along the measuring chamber, and wherein asection of the measuring chamber at the upstream end thereof is taperedinwardly in the direction of fluid flow.

The flow transducer may be used to measure the flow rate of any fluid,but is preferably used for measuring the flow rate of liquids to bedispensed.

According to a still further aspect of the present invention there isprovided a flow transducer comprising a measuring chamber for the fluid,at least one sensor controllable to emit a sound beam into the fluid,and temperature determining means for determining the temperature of thefluid in the measuring chamber.

Preferably, the measuring chamber is elongate and the fluid is arrangedto flow therealong, and an upstream sensor is arranged at a upstream endof the measuring chamber, and a downstream sensor is arranged at adownstream end of the measuring chamber.

Preferably, the measuring chamber diverges in the direction of fluidflow such that the included angle does not exceed 2°. Preferably theincluded angle of the diverging measuring chamber is in the range of0.5° to 1°. In a preferred embodiment, the included angle in 0.67°.

Preferably, the upstream and downstream sensors are arranged such thatsound beams emitted thereby are substantially aligned and pass along acentral longitudinal axis of the measuring chamber.

In an embodiment, the flow transducer has a fluid inlet communicatingwith the measuring chamber to supply fluid thereto, and a fluid outletcommunicating with the measuring chamber to receive fluid therefrom.Preferably, a tortuous path for the fluid is defined between the fluidinlet and the measuring chamber, and between the measuring chamber andfluid outlet, the arrangement being such that fluid is constrained toflow substantially symmetrically across a transmitting face of both theupstream and the downstream sensors.

In an embodiment, the longitudinal axes of the fluid inlet and of thefluid outlet are aligned, and this common longitudinal axis is spacedtransversely from the central longitudinal axis of the measuringchamber.

In an alternative embodiment, the longitudinal axis of one of the fluidinlet and the fluid outlet extends substantially perpendicularly withrespect to the central longitudinal axis of the measuring chamber,whilst the longitudinal axis of the other of the fluid outlet and thefluid inlet extends substantially parallel to, but spaced transverselyfrom, the central longitudinal axis of the measuring chamber.

In a preferred embodiment, each of the sensors comprises a piezoelectricelement arranged, upon the application of electrical signals thereto, toemit an ultrasonic pulse or pulses. The piezoelectric element of eachsensor is also able to receive an ultrasonic sound wave and output aresponsive electrical signal.

In a preferred embodiment, each of the sensors of the flow transducercomprises a sensor as defined above.

Traditionally, sensors incorporating piezoelectric elements utilize suchelements made of a ceramic. However, a ceramic has a poor acousticimpedance match with water, because the density of a ceramic is verymuch higher than that of water. Ceramics also have bell like qualitiesin that the vibrations induced therein persist. Accordingly, in apreferred embodiment of the invention, the piezoelectric element of eachsensor is formed by a PVDF film. Such a film has a density close to thatof water, for example the density is generally of the order of 1.3gms\cc. This means that low energy is required to input the signal intothe liquid, and that there is a fast rise time, that is, the response isgood.

According to a further aspect of the present invention there is provideda flow control valve for controlling the flow of a fluid, the flowcontrol valve having a fluid inlet, a fluid outlet, a main valve membercontrolling communication between the inlet and the outlet, means forbiassing the main valve member into a closed position in whichcommunication between the inlet and the outlet is closed, and means formoving the main valve member against the action of the biassing means toopen the valve, the flow control valve further comprising a pilotchamber which is in communication with the fluid inlet, pressure withinthe pilot chamber being applied to the main valve member in a directionto oppose opening of the valve, and wherein the main valve member isarranged to define a flow path with the outlet, the area of which flowpath varies in dependence upon the position of the valve member andincreases as the valve member is moved in the valve opening direction,and wherein the position of the valve member and hence the rate of flowof fluid through the valve is determined by the moving means.

The flow control valve may be used for controlling the flow of anyfluid, but can particularly be used for controlling the flow of liquidsto be dispensed.

In a preferred embodiment, the means for moving the valve membercomprises a magnetic armature arranged to be moved by the application ofelectrical current to a magnetic circuit. In this respect, the amount ofmovement of the armature is arranged to be substantially directlyproportional to the amplitude of the applied electrical current.

Preferably, the fluid outlet is defined at one end of a tubular memberwhose other end defines a main valve seat, the main valve member beingarranged to abut the valve seat in its closed position, and the mainvalve member having a converging portion extending within the tubularmember. Movement of the main valve member away from the main valve seatis arranged to move the converging portion of the valve member along thetubular member and hence to vary the area of the flow path.

Preferably, means are provided to constrain the converging portion ofthe main valve member to only move longitudinally within the tubularmember. For example, the constraining means may comprise at least threelongitudinally extending vanes, or other projecting means, arranged tocontact the inner surface of the tubular member.

Preferably, the pilot chamber is defined by a diaphragm carried by themain valve member, and at least one aperture is provided in thediaphragm to communicate the pilot chamber and the fluid inlet.

A pilot valve to enable initial opening of the valve and to ensure thatthe main valve member follows the movement of the armature is providedin the pilot chamber. The pilot valve comprises a pilot valve padcarried by the free end of the armature, the pilot valve pad beingarranged to seat on the main valve member to close a pilot boreextending therethrough.

The present invention also extends to a method for dispensing fluids,the method comprising the steps of flowing a fluid to be dispensed to adispensing outlet, sensing the rate of flow of the fluid, andcontinually controlling the quantity and/or the flow rate of the fluiddispensed by way of the dispensing outlet in dependence upon the sensedflow rate.

According to a further aspect of the present invention there is provideda method of dispensing fluids, the method comprising the steps offlowing a fluid to be dispensed to a dispensing outlet, sensing ordetermining at least one physical parameter of the fluid, comparing theparameter(s) sensed or determined with predetermined values, and, if thesensed and determined parameter(s) are outside the predetermined values,locking the dispensing outlet to prevent the dispensing of fluidthereby.

The method according to this aspect of the invention enables adispensing operation to be halted where imitation or substitute fluidsare detected by differences in their physical parameters.

The present invention also extends to a method of testing a fluid, themethod comprising the steps of storing data representative of the speedof sound in a genuine fluid at various temperatures, testing a fluid todetermine information representative of the speed of sound in the testedfluid, and determining information representative of the temperature ofthe tested fluid, and determining if the tested fluid is genuine bycomparing the determined information with the stored data.

In a preferred embodiment, the method further comprises continuallyadjusting the sensed flow rate of the fluid such that the fluid isdispensed by way of the dispensing outlet at a selected flow rate and/orin a selected quantity.

Dispensing the fluid in dependence upon the sensed flow rate, as in amethod of the invention, enables, for example, a selected quantity, tobe reliably dispensed even if the pressure or flow rate of the fluidfalls. This may occur, for example, where the fluid is beingsimultaneously dispensed from a number of outlets.

In an embodiment, a method of the invention may comprise flowing a fluidselectively to a plurality of dispensing outlets, and controlling thequantity and/or the flow rate of the fluid dispensed by way of each ofthe dispensing outlets in dependence upon the sensed flow rate.

In a practical environment, it would generally be carbonated water andconcentrates which are required to be flowed from tubing therefor toselected ones of a number of dispensing outlets.

A method of the invention has particular utility for dispensing post-mixliquids, for example, beverages mixed at the dispensing outlet from morethan one liquid.

In a post-mix embodiment of the invention, the method further comprisesflowing a second liquid to be dispensed to the dispensing outlet,sensing the flow rate of the second liquid to the dispensing outlet, andcontinually controlling the quantity and/or the flow rate of each liquiddispensed from the dispensing outlet in dependence upon its sensed flowrate.

The invention also extends to a method of dispensing mixed fluids, themethod comprising the steps of flowing first and second fluids to bemixed and dispensed to a dispensing outlet, sensing the rate of flow ofeach of the first and second fluids, and continually controlling thequantity and/or flow rate of each fluid dispensed from the dispensingoutlet in dependence upon its sensed flow rate.

In an embodiment, the method further comprises the step of adjusting thesensed flow rate of one or each of the first and second fluids such thatthe mixed fluid dispensed by the dispensing outlet contains the firstand second fluids in selected relative proportions.

Preferably, the first and second fluids are two liquids to be mixed todispense a beverage. For example, the liquids may be water and aconcentrate.

As a method of the invention dispenses two liquids at a quantity or ratedependant upon their sensed flow rates, it enables a mix to be dispensedat a dispensing outlet in which the two liquids are in a predeterminedproportion or ratio.

It may be that the selected relative proportions are required to differ,for example, because different liquids are being dispensed and/or fortaste reasons. A method of the invention can be arranged to vary therelative proportions selected.

In a preferred embodiment of the methods defined above, information asto the selected rate, and/or selected quantity, and/or selectedproportions is supplied to control means, and the sensed flow rate(s)are adjusted by the control means in response to the information.

Preferably, the methods defined above comprise the step of controllingthe quantity and/or rate(s) of the liquid(s) dispensed by way of valvemeans at the dispensing outlet. Generally the valve means are arrangedto be actuated by the control means. For example, where the valve meanscomprises one or more proportional valves, each of the proportionalvalves is actuated by the control means to dispense liquid at a ratedetermined by the control means. The control means varies the rate ofliquid dispensing by the proportional valve as the sensed flow ratevaries.

In embodiments of the methods defined above, the rate(s) of flow may besensed in any suitable manner. Preferably, the sensing of the rate(s) offlow is performed ultrasonically.

According to a further aspect of the present invention there is provideda system for dispensing fluids, the system comprising at least onedispensing outlet, tubing for flowing a fluid to the dispensing outlet,sensing means for sensing the rate of flow of the fluid through thetubing, and flow control means responsive to the sensing means andarranged to continually control the quantity and/or rate of fluiddispensed through the dispensing outlet in dependence upon the sensedflow rate.

The invention also extends to a system for testing a fluid comprisingprocessor means for storing data representative of the speed of sound ina genuine fluid at various temperatures, first determining means fordetermining information representative of the speed of sound in a testedfluid, and second determining means for determining informationrepresentative of the temperature of the tested fluid, the processormeans being arranged to receive the determined information from thefirst and second determining means and to compare then determinedinformation with the stored data.

The dispensing system may include means to lock the dispensing outletwhere imitation or substitute fluids are detected, for example, by thetesting system defined above.

Preferably, said flow control means comprises valve means forcontrolling the flow of fluid through the dispensing outlet, and controlmeans responsive to the sensing means and arranged to actuate the valvemeans.

In a preferred embodiment, the valve means comprises at least oneproportional valve actuable to vary the flow rate of fluid through thedispensing outlet.

Where it is required to dispense mixed liquids, particularly where theliquids in the mixture are to be dispensed in selected relativeproportions, a respective proportional valve may be provided to controlthe flow of each liquid. Preferably, the dispensing outlet is providedat the outlet of a mixing chamber into which each the proportional valvedispenses.

In a preferred embodiment, the proportional valve is as defined moreparticularly above.

The control means is preferably arranged to actuate valve meanscontrolling the flow of a plurality of fluids. In this case, sensingmeans for sensing the rate of flow of each the fluid are preferablyprovided, and the control means is responsive to each sensed rate offlow.

In a preferred embodiment, the control means comprises processor meanshaving an associated memory. Information as to required flow rate(s),required quantity, and/or required proportions of fluids to be dispensedis preferably stored in the memory, and the processor means is arrangedto control the valve means in dependence upon the information stored inmemory and the sensed flow rates.

Preferably, the processor means is also arranged to be responsive touser demands and requirements. For example, the processor means iscoupled to input means arranged to supply demand information.Preferably, the input means comprises a keypad.

In an embodiment, there is a two-way communication between the processormeans and the input means.

The sensing means preferably comprises a respective flow transducer forthe or each fluid to be dispensed. Preferably, each flow transducer isarranged in tubing for flowing the associated fluid to a dispensingoutlet, and preferably, each of the flow transducers is in two-waycommunication with the processor means.

In a preferred embodiment, each of the flow transducers is arranged tosense the flow rate ultrasonically. The processor means is arranged tocontrol the ultrasonic sensing process and to compute the flow rate fromdata provided by the transducer.

In a preferred embodiment, the flow transducer is as defined moreparticularly above.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the present invention will hereinafter be described, byway of example, with reference to the accompanying drawings, in which:

FIG. 1 shows a block diagram of a system for dispensing liquids,

FIG. 2 shows a section through an embodiment of a flow transducer fordetermining the flow rate of a fluid,

FIG. 3 shows a section through a sensor of the transducer of FIG. 2, and

FIG. 4 shows a longitudinal section through an embodiment of aproportional valve for controlling the flow of a fluid.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The drawings illustrate one embodiment of a post-mix dispensing systemfor beverages. Increasingly, beverages, for example, colas and fruitdrinks, are mixed at the point of sale. In this respect a syrupconcentrate is mixed as it is dispensed with carbonated water,Post-mixing has the advantage over pre-mixed beverages that there is nolonger any need to transport the water which makes up the majority ofthe volume Of the beverage, or the containers, which are conventionallyglass bottles or cans, and therefore there are considerable savings intransportation costs. It is also easier to store concentrates thanpre-mixed and packaged beverages, and stock control is also simpler.However, in order to dispense the required beverage, it is extremelyimportant that the concentrate and the carbonated water are mixed in theappropriate proportions. Most concentrates are provided by theirmanufacturers, for example, in a concentration requiring that the finalbeverage be made from five parts carbonated water to one partconcentrate by volume.

In public houses and other venues where beverages are dispensed, it isnow common to provide a facility to pipe carbonated water andconcentrates to one or more dispensing stations which also includemechanical dispensers for at least one concentrate. The dispensingstation is arranged to dispense both the concentrate and the water toprovide a mixed beverage, and the dispensing station tries to keep theflow therethrough relatively constant so that the mixed beveragedispensed has the appropriate relative proportions. However, the knowndevices cannot guarantee that the mixed beverage dispensed reliably hasits constituents in the required proportions. In this respect, thedispensing station will generally be arranged such that the carbonatedwater is dispensed contemporaneously with the concentrate but at a flowrate which is five times that of the concentrate. However, the tubingcarrying the carbonated water and that carrying the concentrates isgenerally of a considerable length so that there is a pressure droptherealong which affects the flow rate therethrough. Traditionally morethan one dispensing station is fed by each carbonated and concentratesupply and the pressure drop at a dispensing station will also varydepending upon whether more than one dispensing station is dispensing atthe same time. The existing mechanical systems, therefore, cannotreliably dispense mixed beverages. Furthermore, the mechanical systemscannot provide a mix of different proportions for different concentratesat the same dispensing station.

Dispensing of the fluids is by way of valves which are turned on and offas required. For example, electrically actuable solenoid valves may beprovided, and there have been proposals to improve the reliability ofthe mix by measuring the fluid flow rates and timing the actuation ofthe valves in dependence thereon.

However, such digital systems are not sufficiently responsive and aresimply not able to react at the speeds necessary to cope with transientsand thus to provide the reliability required.

A dispensing system as described and illustrated in the accompanyingdrawings is able to reliably dispense mixed beverages at the proportionsrequired. It is also able to dispense different concentrates indifferent proportions, and its reliability is not altered if more thanone dispensing station is operated simultaneously. Furthermore, the rateof flow of the beverage can be controlled in dependence upon the portionto be dispensed. This is useful, for example, if it is required todispense a small portion. It is also helpful if a quantity of a beverageis dispensed initially at a slow rate and subsequently at a faster rate,as this prevents splashing and foaming. Again, this is a feature of adispensing system of the invention.

The reliability of the dispensing achieved by the system described andillustrated herein arises out of its ability to respond substantiallyimmediately to changes in the system. This means that the system cancope with transients.

The embodiment described and illustrated below is a dispensing systemfor dispensing mixed beverages such as cola and fruit drinks made from amixture of syrup concentrate and carbonated water. However, it will beappreciated that the invention is not limited to the particular liquidsor beverages which are being dispensed and that the system may be usedfor any dispensing operation required. For example, where a number ofdispensing outlets connected to a common supply tubing are required, adispensing system of the invention can be utilized to ensure that fluidscan be dispensed from one or more of the outlets at similar rates,rather than one outlet being favoured, as occurs in present systems.Additionally and/or alternatively, the system may be used to dispenseany mixed fluid where it is wished to reliably control the relativeproportions of the fluids in the mix.

It will be appreciated that different fluids have different physicalcharacteristics. Proprietary colas, for example, are either imitated ordiluted with water and the imitations have physical characteristicswhich differ from those of the proprietary brands. A system of theinvention can be arranged to detect such variations and this can be usedto control or prevent fraudulent dilution or substitution of imitations.Thus, additionally and/or alternatively a dispensing system of theinvention can be used for any dispensing operation where it is wished toprevent or detect the dispensing of substitute fluids.

For clarity, the description of the embodiments given below refersspecifically to the dispensing of mixed beverages made from syrupconcentrate and carbonated water.

FIG. 1 shows a block diagram of a system of the invention for dispensingbeverages. In the embodiment illustrated in FIG. 1 there are providedtwo dispensing outlets 2,4, the first outlet 2 being arranged todispense a mixed beverage, and the second outlet 4 being arranged todispense carbonated water only. The beverages are dispensed upon thedemand of a user which is input to the system by way of a keypad 8. Thekeypad 8 is in two-way communication with a processor 6 which controlsthe dispensing of the liquid at the outlets 2,4. It will be appreciatedthat the processor 6 may be arranged to access and control many moredispensing outlets than the two which are illustrated.

In the illustrated embodiment, carbonated water, indicated by the arrow10, is arranged to be supplied under pressure to tubing 12. The tubing12 is tapped at a first point so that water may be fed by way of anoutlet valve 14 to the dispensing outlet 4. The tubing is tapped at asecond point so that carbonated water may be fed by way of a furtheroutlet valve 14, and a mixing chamber 16, to the dispensing outlet 2. Asyrup concentrate, indicated by the arrow 18, is arranged to be suppliedby tubing 20 and a further outlet valve 14 to the mixing chamber 16. Inthis way, the beverage dispensed at the outlet 2 can be a mixture of theconcentrate 18 and of the carbonated water 10.

To ensure that the mixture dispensed at the outlet 2 contains theconcentrate and the water in predetermined relative proportions, thevalves 14 for dispensing the concentrate and water are all proportionalvalves and are each controlled by the processor 6. In this respect, theprocessor 6 receives information from respective flow transducers 22 asto the flow rate of the two liquids 10,18, and is arranged to controlthe valves 14 accordingly so that each proportional valve 14 dispenses arequired flow of liquid so as to keep the dispensed mixture reliably inthe required proportions.

The processor 6 may be configured by any suitable means. In anembodiment, the processor 6 is a microprocessor provided with memory,for example an EPROM. The processor 6 is arranged to be connected to themains, as indicated at 24, and a power module 26 for receiving mainspower and powering the processor 6 is provided.

As is indicated in FIG. 1, the processor 6 is also connectible to anhand held terminal (HHT) 5. In this respect, the processor 6 ispreferably provided with one or more communication ports (not visible)to which any required modules, such as the HHT, are selectively, andreleasably, pluggable to communicate with the processor 6.

It is particularly useful to provide for communication between theprocessor 6 and the HHT 5 as such a link can be used to set up thesystem initially. Thus, all the necessary initial values, appropriatedata, and programs can be set up in the factory and downloaded into theprocessor 6. This data may be altered on site utilising the HHT 5 ifrequired.

It is, of course, useful to have the ability to communicate with theprocessor 6, and such an ability can be used for a wide variety ofapplications. For example, means can be provided to link the processor 6with Electronic Point of Sale (EPOS) terminals (not shown) to facilitatereconciliation between sales made and fluids dispensed and/or to provideother control and management information. In such a context, the linkbetween processor 6 and EPOS terminal may be made intelligent.

The memory of the processor 6 is arranged to store information as to therequired flow rate of the liquids controlled by each valve 14. In thisrespect, where a syrup concentrate is to be mixed with carbonated water,it is generally required that the liquids be combined in the ratio of1:5 (concentrate to water). Whilst this dilution is common in thebeverage industry, some concentrates are very difficult to flow at thatconcentration. The system enables such concentrates to be provided in adilute, more flowable, form and for the processor 6 to control themixing of such diluted concentrates in different proportions. In fact,the processor 6 may store a different desired ratio for the mix of eachconcentrate which is to be dispensed.

The flow transducers 22 are described in more detail below. Eachtransducer 22 is arranged to measure the flow rate of the liquid in theassociated tubing 12,20 and to provide flow rate readings to theprocessor 6. It is those values which the processor 6 utilizes tocontrol the appropriate proportional valves 14. The construction of theproportional valves 14 is also described in greater detail below. In apreferred embodiment, each flow transducer 22 is arranged to provideflow readings for the liquid in the respective tubing fifty times persecond.

In the embodiment illustrated, each flow transducer 22 measures thespeed of flow ultrasonically. This requires that ultrasound pulses aregenerated and are transmitted into the flowing liquid. A transducercircuit 28 is associated with each transducer 22 and is arranged togenerate the ultrasound pulses and to make timing measurementstherefrom. This data is then fed by way of the transducer circuit 28 tothe processor 6 so that the processor can determine the flow rate.

Each transducer circuit 28 is associated with, and dedicated to, theoperation of a single transducer 22 whereas the processor 6 receivesinformation from all of the transducers 22. In the embodimentillustrated each transducer circuit 28 is arranged to feed raw data tothe processor 6. However, it will be appreciated that the functions tobe undertaken by the dedicated circuitry 28 and those to be undertakenby the processor 6 can be chosen as required, and depend only upon thecapabilities given to the transducer circuit 28. There may be savings inprocessor time, for example, if, as well as the operational functions,the dedicated transducer circuit 28 undertakes some of the computing ofthe raw data produced.

It is possible to provide a central input means, such as the keypad 8,for enabling the control of a number of dispensing outlets. Of course,an operator will require that the keypad be proximate to the dispensingoutlet being controlled. A single keypad 8 can therefore be providedwhere a number of dispensing outlets are physically grouped together.However, if it is required to space the dispensing outlets at a numberof locations, a number of separate keypads 8, each communicating withthe processor 6 may be provided, each keypad 8 providing the ability tocause liquid to be dispensed from an associated dispensing outlet.

The keypad 8 has a number of keys 30, preferably in the form of membraneswitches, and enables the operator to demand a quantity of a liquid tobe dispensed from an associated outlet, as 2,4. Generally the TradeMark, or logo, or other identification of the drinks to be dispensed ismarked near the keys 30 for simplicity. The operator then only has topress the appropriate key 30 for the required beverage to be dispensed.

It is possible to arrange that actuation of a specific key 30 causes apredetermined quantity of the liquid to be dispensed. However,additionally and/or alternatively, it is possible to require that liquidis dispensed only whilst the appropriate key 30 remains depressed.

Where a key 30 of the keypad 8 is marked with the identification of aparticular beverage, for example "Pepsi" or "Orange", it is generallyarranged that actuating that key alone will cause both the appropriateconcentrate 18 and the water 10 to be dispensed in appropriatequantities into the mixing chamber 16 and hence to the dispensing outlet2.

The mixing chamber 16 may be of any suitable construction. In thisrespect, appropriate mixing chambers for receiving and mixing differentliquids are available currently and may be utilized in the system ofFIG. 1. As the construction of the mixing chamber 16 is not part of thisinvention, it is not further described herein.

Because the rate at which the liquids are dispensed is controlled by thevalves 14 in dependence upon the rates of flow in the tubing 12 and 20,the control of the liquid dispensed is very reliable and reliable mixingof two liquids in selected proportions can be achieved. Furthermore,much more sophisticated control is also possible, as the system can bearranged to provide flexibility to choose the quantity of liquid to bedispensed and the rate at which the liquid is dispensed. In thisrespect, it is useful to be able to control the flow rate depending uponthe amount of liquid to be dispensed. Thus, if only a small portion isto be dispensed, it is normally required that this be done slowly.However, where larger quantities are to be dispensed, for example, tofill a pint of liquid, such quantities need to be dispensed quickly.Even if a large quantity is to be dispensed quickly, it is alsoadvantageous for the flow rate to be profiled so that there is a slowinitial rate which is subsequently considerably increased. This reducesthe risk of splashing. To achieve such control, it is possible toprovide on the keypad keys 30 by which the quantity is determined sothat the dispense is totally under the control of the processor 6.Alternatively, the operator may be allowed to control the dispensing bykeeping the appropriate key 30 depressed. In this case, the processor 6may control the flow to begin slowly, so that a small portion isdispensed slowly. However, if more than a first quantity is dispensed,the processor 6 may then increase the flow rate considerably. The keypad8 has a number of LEDs 32 associated with each key 30. Each LED 32 ispreferably illuminated when a particular key 30 is, or has beendepressed, to indicate the dispensing operation which is beingundertaken.

It has been stated above that the system as shown in FIG. 1 may be usedto control or prevent fraudulent substitution of imitation liquids. Itis not unknown, for example, for the manager of a public house or cafeto buy cheaper imitation colas, rather than the branded versions, or todilute the branded versions with water. However, such imitation colashave physical characteristics which differ from those of the proprietarybrands, and the processor 6 may be arranged to recognise and/or respondto such differences.

The flow rate readings provided by each flow transducer 22 may be thetimes taken by the ultrasonic pulses to travel through the liquidflowing therein between two ultrasound transmitting/receiving faces ofthe transducer. The software of the processor 6 can use this time datato determine the liquid flow rate. If the processor 6 is also providedwith the accurate length of the distance between the twotransmitting/receiving faces it will also be able to accuratelydetermine the speed of sound in the liquid in the transducer.

The speed of sound in a liquid varies with temperature, and a graph ofsound speed against temperature can be obtained, and stored in theprocessor 6, for each proprietary branded liquid the system is set up todispense. Each flow transducer 22 is also provided with temperaturesensing means, such as a thermistor 65, arranged to provide temperaturemeasurements which are, or substantially are, the temperature of theliquid flowing in the transducer 22. The processor 6 is arranged tocompare the determined speed of sound in the liquid at the measuredtemperature with the stored expected value at that temperature. If thedetermined speed is not the same as the stored expected value withinpredetermined tolerances the processor 6 is arranged to provide a signalthat the liquid is a substitution. In this respect, the processor 6 maystore a range of acceptable speed values for the proprietary brand ateach temperature, and/or may store tolerance limits. Generally, a liquidwill be identified as a substitute or fraud if the determined speed isnot within 3 standard deviations of the stored, expected value.

When the processor 6 detects an imitation, such as an imitation cola, itmay be arranged to close down the system, for example by shutting offall of the proportional valves 14. Not only would this require thesystem manager to seek assistance to restart the system, but thedetected imitation cola will remain trapped within the tubing 20, forexample, enabling it to be retrieved for analysis. This fraud detectionapplication of the system is particularly useful where the hand heldterminal 5 is provided, as the terminal can be linked to the processor 6to reset the system in a simple and accurate manner.

FIG. 2 shows a section through one embodiment of a flow transducer 22.As indicated in FIG. 1, the liquid in the tubing, as 12 or 20, isarranged to flow through a respective flow transducer 22. As the liquidflows through the transducer it is subjected to ultrasonic pulsesapplied thereto by two sensors 32. A section through a sensor 32 isshown in FIG. 3.

The sensor 32 illustrated in FIG. 3 is a piezoelectric device which canbe energized to output an ultrasonic waveform, indicated schematicallyat 34, from a central area thereof. The sensor 32 comprises asubstantially cylindrical body 36 of plastics material. This body 36 isreceived within a substantially cylindrical housing 38. In theembodiment illustrated, the housing 38 has a substantially cylindricalperipheral wall 40 which is made of metal and which has at its front endan annular, radially inwardly extending flange 42 which is similarlymade of metal. The body 36 is retained in position within thecylindrical housing 38 by way of crimps or indentations (not shown)formed in the wall 40 to bite into the body 36. The front radiallyextending flange 42 defines a circular opening in the housing 40 acrosswhich a piezoelectric element 48 extends.

The piezoelectric element 48 comprises a circular thin film of PVDFhaving a film of gold deposited over substantially all of its frontsurface. The ultrasonic waveform 34 is generated by applying anelectrical potential across the thickness of the piezoelectric element48 by way of a metal contact post 53. This contact post 53 is providedwith a flat, substantially circular contact surface which is held inabutment with the rear surface of the piezoelectric element 48. Thus,the circular contact surface of the post 53 opposes and overlies acorresponding area of the gold film on the front surface of the element48 and it is these aligned conductive areas which apply the electricalpotential across the element 48 and thereby define a circular area ofthe sensor 32 from which the ultrasonic waveform 34 is emitted. In thisrespect, in the circular, substantially central area of the element 48,where the gold film is aligned with the contact surface of the contactpost 53, mechanical vibrations caused by the piezoelectric effectgenerate the ultrasonic waveform. With the present invention, thewaveform generated is a series of ultrasonic pulses.

The necessary electrical connections are made to the front surface ofthe piezoelectric element 48 by way of the housing 38. In this respect,it will be appreciated that the radial flange 42 surrounds and is incontact with the circumference of the gold covered front surface of theelement 48. Preferably, a conductive paste, not visible, is insertedalong the area of contact between the flange 42 and the gold coveredsurface to enhance the connection. The electrical connection to thehousing 38 is made by way of a metal clamp 74 which is shown in FIG. 2.

The sensor 32 shown in FIG. 3 is extremely simple to make. The contactpost 53 is a generally cylindrical post having a reduced diameterportion 52 defining a key portion for retaining the post 53 with thebody 36. At its end projecting rearwardly of the cylindrical body 36,the contact post 53 is tapped to form a cylindrical longitudinallyextending bore 54 which is internally screw threaded, at least at itsouter end. The contact post 53 is also knurled on a part 55 of its outersurface.

The contact post 53 is moulded into the cylindrical body 36. Thus, thepost 53 is positioned in a mould for the body 36 and then the plasticsmaterial is formed therearound. The reduced diameter portion 52 acts tokey the post 53 in position, and this key portion and the knurling onthe outer surface part 55 of the post 53 prevent axial movement androtation of the post 53 relative to the plastics material body 36. Aftermoulding, the front surface of the combined body 36 and post 53 ismachined flat. This is necessary to ensure that the piezoelectricelement 48 when adhered to the front surface is reliably in contact withcontact surface of the post 53. It will be appreciated that the post 53forms the electrode for the sensor 32, and an electrical terminal (notshown) can be connected thereto by screwing it into the bore 54.

Once the plastics material body 36 and post 53 have been assembled, thepiezoelectric element 48, to the front surface of which the gold filmhas been bonded, is adhered to the machined front surface of theassembly. The resultant assembly is then inserted into the cylindricalhousing 38 so that the gold film of the element 48 is in electricalcontact with the flange 42. The assembly of the sensor 32 is completedby crimping or otherwise indenting the peripheral wall 40 of the housing38 to hold the assembly together.

The contact post 53 is made of a metal which is particularly rigid andacts, when electrical potential is applied across the element 48, toprovide a high acoustic impedance so that the ultrasonic pulse is sentinto the liquid. Preferably, the post 53 is made of stainless steel

As will be apparent from FIG. 2, the liquids whose flow rate is to bemeasured by the transducer 22 will come into contact with the frontsurface of the piezoelectric element 48 of the sensor 32. For thisreason, the electrically conductive film used on the front surface ofthe element 48 is preferably gold as this is inert. However, it is alsopreferred that a film of a food approved barrier material (not shown) isbonded to the front surface of the element 48. Furthermore, and as isshown in FIG. 3, an O ring 46 is mounted in the opening defined by theflange 42 to seal the sensor 32 against the ingress of liquid.

The simple construction of the sensor 32 illustrated in FIG. 3 lendsitself to mass production. The construction is very much simpler thanprior art sensors, for example used in scientific apparatus, but is hasbeen found that its performance is more than adequate for a system ofthe invention.

Two of the sensors 32, as described above, and as illustrated in FIG. 3,are incorporated in the flow transducer 22 which is illustrated in FIG.2. As can be seen, the flow transducer 22, which is preferablyfabricated of a plastics material, comprises a liquid inlet 60 to whichtubing, as 12,20, is connected, and a liquid outlet 62 which issimilarly connected to the tubing, as 12,20. Thus, it will beappreciated that liquid in the tubing enters the transducer 22 throughthe inlet 60, flows through the transducer, and subsequently flows outof the transducer by way of the outlet 62. Between the inlet 60 and theoutlet 62 the transducer is provided with a measuring bore or chamber 64through which the liquid has to flow. In the illustrated embodiment, themeasuring bore 64 is a longitudinally extending bore of circularcross-section which, at each of its ends, faces the front of arespective sensor 32. The centre line of the bore 64 is aligned with thecentre of the central emitting area of each sensor 32. This means thatsound beams emitted by each sensor 32 are aligned with, and travelalong, the central longitudinal axis of the measuring bore 64.

Preferably, the transducer 22 has a housing 68 which is moulded in onepiece from a suitable plastics material, such as acetal. As a liquid isto be flowed through the transducer 22 it is advantageous that thehousing 68 is made from only a single moulding. The provision of asingle moulding means that there are no interconnected parts and thusthat there are no sealing problems associated therewith.

As described above, the housing 68 defines a measuring bore 64.Furthermore, two opposed cylindrical recesses 66 are defined in thehousing 68 in each of which a respective sensor 32 is received. Thearrangement is such that each sensor 32 can be mounted so that thefront, beam emitting surface thereof, defined by the front surface ofthe piezoelectric element 48, is spaced from the adjacent end of themeasuring bore 64. The emitting surfaces of the sensors 32 form thetransmitting/receiving faces of the transducer 22 referred to above.

In the illustrated embodiment, the thermistor 65 for measuring thetemperature of the liquid in the measuring bore 64 extends within anarrow bore moulded in the housing 68. The temperature sensitive head ofthe thermistor 65 is arranged to be separated from the measuring bore 64by only a very thin layer of the plastics material and is inserted insilicone grease. The thermistor 65 is thus in good thermal contact withthe liquid in the measuring bore 64.

The liquid inlet 60 has a longitudinal axis which extends substantiallyperpendicularly to the centre line of the measuring bore 64 whereas theaxis of the outlet 62 is substantially parallel to the centre line ofthe measuring bore 64 but laterally offset relative thereto. Thisarrangement forces liquid flowing into the transducer 22 to take atortuous path into the measuring bore 64, this path causing the liquidto flow symmetrically across the front surface of the sensor 32 at theupstream end of the bore 64. Similarly, liquid leaving the measuringbore 64 follows a tortuous path to the outlet 62, and again thistortuous path takes the liquid across the front surface of thedownstream sensor. This tortuous path is important in providing therequired type of liquid flow through the measuring bore 64, as describedbelow.

It will be seen that there is provided in the liquid inlet 60 a gauzefilter 70 to remove any contaminants from the liquid. It will also beseen that in the embodiment of FIG. 2 the tubing 12, 20 is provided withan appropriate shaped end for insertion into the inlet 60, that endcarrying an appropriate O ring seal 72. The tubing 12, 20 may be a pushfit in the inlet 60 and/or secured therein by any suitable means (notshown).

The outlet 62 is defined by an extension pipe 76 which, in thisembodiment, is moulded separately from the housing 68 and affixedthereto by any suitable means. A respective O ring 78 ensures that thejoint between the pipe 76 and the housing 68 is appropriately sealed. Inmoulding the relatively complex shape of the housing 68 it may benecessary to have a bore, as 77, accommodating a moulding core. This issimply sealed by pressing a glass ball 79 therein.

The geometry of the housing part 68 of the transducer 22, andparticularly of the flow paths for the liquid is important in providingthe appropriate flow along the measuring bore 64. It would be possibleto arrange that the liquid flow along the measuring bore 64 issubstantially laminar. However, and as is well known, different parts ofa flow travel at different velocities and with laminar flow thedifference in velocity between that at the centre line and that at theperiphery of the bore 64 is very marked. More importantly, the nature ofthe liquid flow along the measuring bore 64 will change as the liquidmoves along the bore and approaches the laminar profile, and this causeschanges in the centre line velocity. It is preferred that the flow alongthe measuring bore 64 have a fairly uniform centre line velocity.

The flow which is achieved is the result of the geometry of the flowpath and it will be seen that at its inlet the measuring bore 64 has aninwardly tapering section 63. This tapering section 63 is shaped so thatit does not introduce turbulence into the liquid as it enters the bore64. For the same reason, the external rim of the tapering section 63 hasa gently curved profile and is not truncated. This rim profile shapealso acts to avoid the introduction of turbulence into the liquidentering the measuring bore 64.

The tapering section 63 leads into the measuring bore 64 which islongitudinally extending and circular in cross-section. However, thebore 64 does not have a constant cross-sectional size along its length.Instead, the bore 64 tapers outwardly along the direction of flow, thatis, it diverges towards its outlet end. It has been found that thisgentle taper holds the flow and ensures that it has a fairly uniformcentre line velocity. The taper must be gentle, and it is preferred thatit does not exceed a 2° included angle. Preferably, the included anglewill be in the range of 0.5° to 1°, and it has been found that anincluded angle of 0.67° is particularly effective.

The ultrasonic beam 34 generated by each sensor 32 is confined in width,and for example, is of the order of 4 mm in diameter. Each beam 34 isaligned with the central axis of the measuring bore 64. This ensuresthat the flow rate measured by the transducer 22 will be substantiallythe centre line velocity, which, as we have seen, is arranged to besubstantially constant. Thus, the effect of any friction at theperiphery of the bore 64 is ignored.

It is important to hold the flow in a substantially known shape and toavoid the introduction of turbulence into the flow as this makes itpossible mathematically to compute the flow. Such computation isnecessary in order to provide the appropriate information about flowrates to the processor 6.

The method by which the transducer 22 enables the flow rate of theliquid through the bore 64 to be measured is generally known and willnot be described in great detail. Briefly, an electrical pulse isapplied to the upstream sensor 32 such that an ultrasonic pulse isemitted thereby and travels along the bore 64 with the liquid flow. Thetime taken by the ultrasound pulse to reach and be sensed by thedownstream sensor 32 is measured. An electrical pulse is then applied tothe downstream sensor such that, in its turn, it emits an ultrasoundpulse which travels upstream in the bore 64 against the flow. Again, thetime between firing of the pulse and it being received by the upstreamsensor is measured. It will be appreciated that from the two timemeasurements made, the speed of the flow of the liquid within themeasuring bore 64 can be determined.

In the embodiment illustrated, a printed circuit board 73 is carried bythe housing 68 of the transducer and is arranged to control theapplication of electrical pulses to the sensors 32 and to detect thereceipt of ultrasonic pulses. The thermistor 65 is also connected to theprinted circuit board 73 so that temperature measurements can besupplied to the processor 6. It will be seen that the housing 68 and theprinted circuit board 73 are interengaged. It will also be appreciatedthat the metal clamp 74 at each end of the transducer 22, to contact thesensor housings, and the contact post 53 can be electrically connectedto the printed circuit board 73 to receive power therefrom. For example,a wire (not shown) connected to the circuit board 73 can be electricallyconnected to the clamp 74 by way of a screw also used to hold the metalclamp 74 in position relative to the housing 68. Thus, the metal clamp74 not only holds a respective sensor 32 in position, but also makes thenecessary electrical connection therewith. The printed circuit board 73may carry the transducer circuit 28 (FIG. 1) which is arranged tocontrol the firing of ultrasonic pulses. The circuit board 73 will alsobe connected, for example, by way of the transducer circuit 28, to theprocessor 6. By this means, the time taken for ultrasonic pulsestravelling upstream and downstream within the measuring bore 64 can befed to the processor 6 which is thereby enabled to compute the flow rateof liquid through the bore 64. The information and the computations madetherefrom are used to control the dispensing of liquid by way of theproportional valves 14.

The software within the processor 6 enabling the computations to be madeis within the competence of any one skilled in the art and is notfurther described herein. However, it is important to note that in orderto obtain a fully responsive dispensing system, it is necessary for theflow rate to be determined regularly, for example fifty times a second.

In the embodiment illustrated, housing 68 of the transducer 22 is formedin one piece. Of course, it is possible for the housing to be made inmore than one piece with the individual parts appropriately heldtogether. With such a construction, parts of the transducer where liquidflow is not required are sealed by way of appropriate O rings.

The processor 6 is, as we have seen, able to determine the rate of flowof any liquid as 10,18 in its tubing 12,20. In response to the flow ratedetermined, and in response to the instructions received from the keypad8, the processor 6 actuates an appropriate proportional valve 14 todispense the liquid to a dispensing outlet 2 or 4. In this respect, toensure that the system is fully responsive, the proportional valves 14are constructed to change the rate at which liquid is dispensed infractions of a second.

A longitudinal section through one embodiment of a proportional valve 14is shown in FIG. 4. This valve 14 includes a movable magnetic armature80 and it is the position of this armature which, as will be clear fromthe description below, determines the rate of flow of liquidtherethrough. The armature 80 is preferably made of magnetic stainlesssteel and is in the form of a dumb-bell having radially extending polepieces 82 at each end thereof. The armature 80 is slidably mountedwithin a generally cylindrical housing 84 having a base 86. At its endnearest to the base 86, the armature 80 has a longitudinally extendingbore 88 in which a spring 90 is mounted. The spring 90 acts to bias thearmature 80 away from the base 86. Preferably, and as illustrated, thehousing 84 is formed to have a central post 85 extending away from thebase 86 substantially axially to locate and guide the spring 90 and toact as a stop for the upward movement of the armature 80.

Two annular pole pieces 92 and 93 are mounted to extend around thehousing 84 and are separated by a coil 94 which is connected by way ofleads 96 to receive electrical power under the control of the processor6. A cylindrical sleeve 98 of mild steel is positioned around the polepieces 92, 93 and the coil 94 to provide a return path for the magneticcircuit. The leads 96 extend through a recess 95 provided in the sleeve98.

In the position of the armature 80 shown in FIG. 4, which is theposition thereof determined by the spring 90, it will be seen that theupper pole piece 82 of the armature is displaced from the correspondingupper pole piece 92. The lower pole pieces 82 and 93 remain overlappedto feed magnetic flux into the magnetic circuit. It will be appreciatedthat if current is fed to the coil 94 at a sufficient amplitude toovercome the force of the spring 90, the magnetic field generatedthereby and appearing in the upper pole pieces 92 will be sufficient toattract the corresponding upper pole piece 82 of the armature.Furthermore, once the initial bias has been overcome, increasing thecurrent and hence the magnetic field, increases the attractive forces.It can be shown that the amount of movement of the armature pole piece82 towards the pole piece 92 is directly proportional to the amplitudeof the applied current. Of course, once the pole pieces 82 and 92 arealigned, no further movement of the armature 80 will take place.However, the armature 80 will generally have come into abutment with thestop 85 before this happens.

Of course, it will also be appreciated that the armature 80 cannotsimply be used to control the opening of a valve member to provide aproportional flow of a fluid. In this respect, as soon as the armature80 moves sufficiently to allow a valve member to open slightly, thepressure force of the fluid on the armature 80 drops and acts to furtheropen the valve member and to move the armature irrespective of theamplitude of the current applied thereto. To overcome this problem, thevalve 14 shown in FIG. 4 provides for that liquid to be controlled andto be applied to the valve member both in a direction to open the valveand in an opposing direction. As the liquid forces are thereby balanced,the opening of the valve can be determined solely by the electricalsupply applied to the magnetic circuit. Furthermore, in a valve of theinvention, the valve member is shaped that the further it moves awayfrom its closed position the greater is the area of the flow path forliquid. Thus, the flow rate of liquid through a valve of the invention,at a given pressure, is substantially directly proportional to theamplitude of the electrical current supplied.

As shown in FIG. 4, the armature 80 has a pad 100 received within acorresponding bore formed in its projecting end. The surface of the pad100 defines a valve seat and, in the closed position of the valve, thevalve seat engages an end of a main valve member 102 in which a pilottube 104 opens. In this respect, it will be seen that the pilot tube 104extends through the main valve member 102. The main valve member 102controls the communication between a liquid inlet port 106 and a liquidoutlet port 108. The outlet port 108 is provided at one end of a tubularmember 110 at whose other end the main valve seat 112 is defined. Itwill be seen that a longitudinal bore extends through the tubular member110. An external annular groove is provided in the tubular member 110and receives a securing disk or circlip 114. The securing disk 114together with an outwardly extending flange provided on and surroundingthe main valve seat 112 securely fastens the tubular member 110 on avalve body 116 in which the inlet port 106 extends.

Between the open end of the housing 84 and the valve part 116 adiaphragm 118 is secured. This diaphragm 118, which is also received inan annular groove of the main valve member 102, defines a pilot chamber120. A small hole (not visible) extends through the diaphragm 118 suchthat liquid at the inlet port 106 of the valve enters and fills thepilot chamber 120.

In the closed position of the valve 14, which is shown in FIG. 4, liquidunder pressure at the inlet 106 passes through the hole in the diaphragm118 into the pilot chamber 120 and therefore acts on both surfaces ofthe diaphragm 118. In this position, the spring 90 and the pressureacting on the main valve seat 112 keeps the valve closed. If an electriccurrent is then applied to the coil 94 and is sufficient to overcome theforce of the spring 90 and all of the other small forces acting to keepthe pilot valve closed, the magnetic forces will move the armature 80against the action of the spring and other forces in a direction to openthe valve. In this respect, it will be appreciated that as well as theforce of the spring 90, there will be liquid pressure acting to keep thepilot valve closed as well as forces of gravity and friction and thelike. The opening movement, of course, is upwardly, as is shown in FIG.4.

As the armature 80 begins to lift, the valve pad 100 carried thereby islifted from the end of the pilot tube 104 and liquid in the pilotchamber 120 flows through the tube 104 in the main valve member 102 andto the outlet port 108. This flow reduces the pressure in the pilotchamber 120 as compared to the pressure on the other side of thediaphragm 118, and hence the diaphragm 118 begins to lift away from themain valve seat 112 and in doing so lifts the main valve member 102.Flow of liquid from the inlet port 106 to the outlet port 108 throughthe main valve seat 112 therefore commences. However, the pilot chamber120 remains in communication with the liquid inlet 106 via the smallhole in the diaphragm 118. As the upwardly moving main valve member 102approaches pad 100 the flow into the pilot tube 104 is reduced.Automatically a balance point is established where all forces acting oneither side of the diaphragm 118 are equal so that it remains stationaryat the position dictated by the pad 100 carried by the armature 80.Movement of the armature 80 therefore continues to a position which isdetermined by the amplitude of the electrical current applied to thecoil 94. As the armature 80 moves upwardly, it causes the valve member102 to move upwardly in the same manner by a repetition of the processdescribed above on initial opening. Thus, it will be appreciated thatthe valve member 102 moves upwardly by a distance which is substantiallyequal to the movement which has been undertaken by the armature 80.

The valve member 102 has a converging cross-section and thus as it liftsout of the tubular member 110 the area of the flow path it defines withthe bore 108 thereof increases. It will thus be seen that the valveshown in FIG. 4 acts substantially as an accurate proportional valve.Thus, the amplitude of the current applied to the coil 94 determines theposition of the armature 80 and hence of the valve member 102. Thefurther the valve member 102 is removed from the tubular member 110 thegreater is the area of the flow path. Thus, the flow at a given pressureallowed by the valve is substantially directly proportional to theamplitude of the current supplied. This can, of course, be used toensure that the liquid dispensed by the system of FIG. 1 is alwaysreliably determined by the electrical control signals applied thereto bythe processor 6.

Of course, the amplitude of the current supplied to the coil 94 can bechanged substantially instantaneously under the control of the processor6 to respond to demands for high or lower rates of flow or for increasedor decreased liquid quantities. The flow dispensed by the proportionalvalve 14 of FIG. 4 can similarly be changed in a fraction of a second inresponse to a change in the current amplitude.

For any given pressure, it is the position of the valve member 102relative to the bore 108 which determines the flow through the valve 14.Of course, the flow rate will depend upon the pressure of the liquid,but the valve 14 is controllable to provide exactly the quantity ofliquid required irrespective of the pressure of the liquid flowing intothe inlet 106. Thus, if the pressure of the incoming liquid falls, sothat the flow rate in the tubing also falls, an increase in the currentamplitude applied to the coil 94 will open the valve 14 further toincrease the flow rate therethrough. Of course, it will be appreciatedthat the flow rate through the valve 14, and hence through the tubingconnected thereto, is detected by an appropriate transducer 22.

The amount of taper of the tapering external surface of the valve member102 can be chosen as required. This tapering external surface alsocarries a plurality of longitudinally extending vanes (not shown) whichproject radially and increase in their radial extent as the radius ofthe external profile of the valve member 102 decreases. This means thatthe longitudinally extending surfaces of the vanes contact the interiorsurface of the bore 108 along their entire length. The vanes thereforeensure that the valve member 102 is constrained to move substantiallylineally along the longitudinal extent of the bore 108 and the vanesprevent any twisting movement of the valve member 102.

In the above description, the flow transducer, the sensor, and theproportional valve have all been described in conjunction with adispensing system for beverages. Of course, each of these components maybe used alone or in alternative systems and none of these components islimited in application to the system of the invention.

It will be appreciated that particular components of the system, and thesystem as described and illustrated, are provided by way of example onlyand various modifications and variations may be made thereto within thescope of this application.

I claim:
 1. A system for dispensing fluids, said system comprising atleast one dispensing outlet, tubing for flowing a fluid to saiddispensing outlet, sensing means for sensing the rate of flow of saidfluid through said tubing, and flow control means responsive to thesensing means and arranged to continually control at least one of thequantity and the rate of fluid dispensed through said dispensing outletin dependence upon the sensed flow rate, said flow control meanscomprising valve means for controlling the flow of fluid through saiddispensing outlet, and control means responsive to said sensing meansand arranged to actuate said valve means, and said valve meanscomprising at least one flow control valve actuable to vary the flowrate of fluid through said dispensing outlet said flow control valvehavinga fluid inlet, a fluid outlet, a main valve member controllingcommunication between said fluid inlet and said fluid outlet, the mainvalve member being movable between a closed position in whichcommunication between said fluid inlet and said fluid outlet is closedand positions in which the valve is open allowing communication betweensaid inlet and said outlet, the fluid pressure at the fluid inlet beingapplied to said main valve member in a direction to open said valve,means for biasing said main valve member into its closed position, andmeans for moving said main valve member against the action of saidbiasing means to open the valve, the flow control valve furthercomprising a pilot chamber which is in communication with said fluidinlet, the fluid pressure within said pilot chamber being applied tosaid main valve member in a direction to oppose opening of said valve,and said main valve member being to define a flow path with said fluidoutlet, the area of said flow path varying in dependence upon theposition of said valve member and increasing as the valve member ismoved in the valve opening direction, fluid pressure being applied tosaid main valve member in both opening and closing directions whereby,when the valve is open, the position of the valve member and hence therate of flow of fluid through the valve is determined by said movingmeans, said valve further comprising an elongate tubular member having alongitudinal axis and first and second ends spaced along saidlongitudinal axis, said first end of the tubular member defining atubular main valve seat, and the second end of the tubular memberdefining said fluid outlet, the main valve member extending within saidtubular member, and said main valve member being elongate and having alongitudinal axis extending coaxially with the longitudinal axis of thetubular member, and having a first portion with a peripheral wallextending substantially parallel to the longitudinal axis thereof, saidfirst portion of said main valve member extending within said tubularmain valve seat in its closed position, and said main valve memberhaving a second portion, following said first portion, having aconverging cross-section, movement of the main valve member along itslongitudinal axis in the valve opening direction moving the firstportion out of said tubular main valve seat to open the flow paththrough the main valve seat, and further movement of the main valvemember in the valve opening direction moving the second, convergingportion of the valve member along the tubular member thereby varying thearea of said flow path.
 2. A dispensing system according to claim 1,constructed and arranged to dispense mixed liquids in selected relativeproportions, a respective flow control valve being provided to controlthe flow of each liquid.
 3. A dispensing system according to claim 2,wherein said dispensing outlet is provided at the outlet of a mixingchamber into which each said flow control valve dispenses, and whereineach flow control valve is a proportional valve.
 4. A dispensing systemaccording to claim 1, wherein said control means comprises processormeans having an associated memory, information as to the required flowrate, required quantity, and required proportions of fluids to bedispensed being stored in said memory, and wherein said processor meansis arranged to control said valve means in dependence upon theinformation stored in memory and the sensed flow rates.
 5. A dispensingsystem according to claim 4, wherein said processor means is coupled toinput means arranged to supply demand information and is responsive tosaid demand information.
 6. A dispensing system according to claim 1,wherein said sensing means comprises a flow transducer for the fluid tobe dispensed, the flow transducer being arranged in tubing for flowingthe fluid to said dispensing outlet, and said flow transducer being intwo-way communication with said control means.
 7. A dispensing systemaccording to claim 6, wherein said flow transducer is constructed andarranged to sense the flow rate ultrasonically.